1. Field of the Invention
The present invention relates generally to collision avoidance systems. More particularly, the present invention provides an on-board traffic collision avoidance system, including a computer and programming instructions, which utilizes GPS position data to avoid collisions between vehicles. The invention is particularly useful in air traffic control.
2. Description of the Related Art
The global positioning system (GPS) is a constellation of twenty-four satellites that orbit the earth twice a day, transmitting precise time and positioning information to anywhere on the globe, twenty-four hours a day. The system was designed and deployed by the U.S. Department of Defense to provide continuous, worldwide position and a navigation data for the use of the United States and allied military forces. The potential for commercial applications of GPS were recognized early in the system's development and a determination made to allow free access to GPS signals with certain constraints applied.
Each GPS satellite broadcast two signals, PPS (Precise Positioning Service) and SPS (Standard Positioning Service). The PPS signal is an encrypted military-access code. The SPS is an unencrypted, spread-spectrum signal broadcast at 1,575.42 MHz. Unlike signals from Land-base navigation systems, the SPS signal is virtually resistant to multi-path and nighttime interference, it is unaffected by weather and electrical noise.
GPS receivers listen to signals from either three or four satellites at a time and triangulate a position fix using the interval between the transmission and reception of the satellite signal. Any particular receiver tracks more satellites than are actually needed for a position fix. The reason for this is that if one satellite becomes unavailable, the receiver knows exactly where to find the best possible replacement. Three satellites are required for two-dimension positioning (i.e. position only). Four satellites are required for three-dimension positioning (i.e. position and elevation). In general, an SPS receiver can provide position information with an error of less than twenty-five meters and velocity information with an error of less than five meters per second. A PPS receiver permits much greater accuracy. The higher accuracy is obtainable with the GPS make it suitable as a precision survey instrument.
Collision avoidance is a general problem in the operation of virtually any type of vehicle. The problem is particularly acute in the aviation industry. This is in part because of the significant number of both commercial and private aircraft and the fact that any collision between aircraft can result in a significant loss of life.
At present, general aviation pilots (i.e., private pilots) depend on air traffic controllers and their own observations to avoid collisions. Near misses occur regularly, even when the pilots are under FAA control.
Most commercial aircraft today are equipped with a collision avoidance system. However, such systems are often bulky and expensive to purchase and maintain. The systems do not utilize GPS data. It has been proposed to replace the current collision avoidance systems in commercial aircraft with a system which utilizes GPS data. The system proposed by the FAA would have information relating to the global position of aircraft in a particular vicinity transmitted to a centralized FAA control station by each aircraft within the vicinity and then retransmitted by the central control center to all other aircraft in the vicinity. The central FAA control concept facilitates the monitoring of a large number of aircraft over a very large area of perhaps 200 square miles or more. A centralized facility also facilitates the use of large, high-powered computers which can process large amounts of information quicker and perform more functions, such as making long-range predictions of potential problems, than on-board computers. However, a problem exists with the proposed system in that if the central control station has a failure or outage, the global position information relating to aircraft in the vicinity would not be received and hence could not be monitored or retransmitted.
Even if the FAA proposed system is implemented, it will not solve the problem of aircraft flying without their location transponders activated. In some cases, the aircraft crew has failed to turn on the transponder, while in other cases the transponder has been left in a standby state. After the aircraft has landed, there is an equally high incidence of transponders being left on.
The proposed FAA system does not deal with the problem of general aviation aircraft which may not have transponders.
Before beginning a flight, pilots may file a flight plan. Upon arrival, it is the pilot's responsibility to close the flight plan. A continuing problem, which again will not be solved by the FAA's proposed system, is that pilots fail to close out flight plans. When this occurs, a search mission may be unnecessarily begun after the scheduled arrival time, only to find the pilot safe in an airport coffee shop. Hence, the pilot's failure to promptly close the flight plan upon arrival can result in unnecessary expense and consternation.